The invention relates to a method for determining the absolute position of an element mobile in reference to two magneto-sensitive sensors, with a source for a magnetic field being fastened thereat, with its magnetic features being determined via the magneto-sensitive sensors such that a first sensor signal is measured with a first magneto-sensitive sensor and a second sensor signal with a second magneto-sensitive sensor. Here, the sensor signals representing a component of the magnetic field show a phase off-set φ amounting to 0°<φ<180° or 180°<φ<360°.
Here, in the following magneto-sensitive sensors shall particularly include Hall sensors and magneto-resistive sensors.
The invention also relates to a device for a touchless detection of a relatively mobile element comprising a source for a magnetic field fastened on the mobile element.
Due to its robustness and long lifespan the touchless determination of the absolute rotational position of a mobile body is required primarily in sensors of the automotive industry, industrial automation, devices of medical technology, and the consumer industry.
The touchless detection of the absolute angle of rotation of a rotationally supported magnet and a measuring principle based on Hall sensors is described in various patent publications.
DE 698 16 755 T2 (Austria Mikrosysteme, Jun. 3, 2004) describes a method determining the signals required for calculating the rotational position by forming the difference from two Hall sensor groups. In this method it is disadvantageous that three or four sensors are required and the device described requires an axial design in which the Hall sensors are located underneath the rotationally supported magnet.
A determination of the position of rotation by assembling the sensor at the perimeter of the source of the magnetic field, as described in this publication of an invention, is impossible using the method according to DE 698 16 755 T2, because the sensor must be fastened centrally in reference to the axis of rotation.
WO2009088767A2 (Allegro Microsystems, Jul. 16, 2009) describes two embodiments. The first embodiment (FIG. 1-47, claims 1-12) describes a design, which determines the absolute angular position via 2 or 4 Hall sensors arranged underneath the source of the magnetic field, measuring the axial magnetic field. The signal processing occurs analog. In this embodiment again an analog method is described to correct the phase off-set, with the phase off-set here must amount to 90°<φ<180°.
A second embodiment, WO2009088767A (FIG. 48-55, claims 13-29) describes a design in which the sensors are fastened at the perimeter of the source of the magnetic field and measure the radial magnetic field. However, here three or four Hall sensors are required.
The method described in the publication of the uses only two Hall sensors for this type of measurement.
WO200004339 A1 (Unique Mobility Inc., Jan. 27, 2000) describes a design in which two Hall sensors are fastened at the perimeter of the source of the magnetic field such that they detect the tangential magnetic field. Furthermore, the sensors are arranged such that the measured signals show a fixed phase off-set of 90°.
Here, it is disadvantageous that the phase off-set can change by imprecisions in positioning when the Hall sensors are assembled. This error is not compensated. Furthermore, this design requires two linear Hall sensors in separate housings.
WO2008/077861 (ZF Lenksysteme, Jul. 3, 2008) describes a design in which two Hall sensors are fastened at the perimeter of a two-polar magnetized magnetic field source such that they detect the radial magnetic field. The sensors are arranged such that they show a fixed phase off-set of 90°.
Here, it is disadvantageous that the phase off-set can change by imprecisions in positioning when the Hall sensors are assembled. This error is not compensated. Furthermore, this design requires two linear Hall sensors in separate housings.
In order to achieve a phase off-set of 90° the sensors must be positioned precisely at a distance of a quarter rotation of the source of the magnetic field, resulting in relatively large space required.
US20080290859 (Timken Corp. Nov. 27, 2008) describes a design in which the absolute position of a linearly moved object or a rotational object can be determined using a multi-polar magnet. For this purpose, a group of several Hall sensors positioned serially is switched such that here a sinusoidal and a cosine signal result. Here, phase off-sets of the signals caused by the different polar lengths in reference to the length of the sensor group can be compensated via adjustments of amplification.
In this method it is disadvantageous that the absolute position can only be determined within a terminal pair of the multi-polar magnetic field source. A direct absolute determination of position over a full rotation of 360° is not possible with this method.
In US20100194385 (Moving Magnet Technologies, Aug. 5, 2010) the absolute position at the perimeter of a source of the magnetic field is determined by one sensor detecting both the radial as well as the tangential magnetic field. From these signals, naturally in their phase off-set by 90°, then the absolute angular position is calculated.
By the measurement of both the radial as well as the tangential magnetic field particular sensor types are required (lateral Hall sensors with ferromagnetic field concentrator, see Co. Melexis, Trademark Triaxis®).
Due to the sensitivity of the magnetic fields in 2 axes (x and y, respectively radial and tangential field), the sensors are sensitive regarding external magnetic fields interference.
The invention is based on the objective to provide a method for the determination of the absolute position of a mobile element, which is reliable and operates safely.
The invention is further based on the objective to provide a device to implement the method according to the invention.